Process for detecting insect contamination of foodstuffs by fluorescence



March 18, 1958 R. K. LADIscH PROCESS FOR DETECTING INSECT CONTAMINATION 0F FOODSTUFFS BY -FLUORESCENCE Filed Dec. 14, 1954 INVENTOR R K. Lczydisch,

Armen/5y.

.N .GNN N United States Patent O PROCESS FOR DETECTING. INSECT CONTAMINA- TION OFFOODSTUFFS BY FLUGRESCENCE Rolf Karl Ladis`hLansdowne, Pa.

ApplicatiorrDecember14,1954, Serial No. 475,322

3 Claims. (Cl. 23-23) (Granted vundervlitle 35, U.S. Code (1952), sec. 266) The invention described herein, if patented, may be manufactured and used by or lfor lthe 4Government for governmental purposes without the payment of any royalty thereon.

This invention relates to the detection of insect contamination'in wheat flour and like foodstuis `by iluorescence. i

Insect infestation of grain and grain products has-long been a serious problem because of economic losses. Within the past few years, attention has been focused on this subject because Yof insistent demands 4for food sanitation. 'See-Gray,-H. E., ,Food'in Canada, 10, 1l (1950);fHerford, V. G., RoypSan. Inst. (London), 73, 412 (1953); 'KayyI-I. D., ibid.,'73, 405 l(1953); Makin, A., ibid. 73, 408 (1953); Hearings, Comm. Agr. Forestry, U. "S, Senate, '83rd Congress lst Sess., ,Grain- Sanitation :Program of the Food and Drum .Administration, Government :Printing Oice, 1953.

A number of researches in this -leld'have resulted in such patents as Frankenfeld, 2,525,789, dated October 17, 1950, andLarkin, 2,639,617, dated 4May 26, 1953, both involving staining procedures; while Johnson, RK. (Food Engin., 1952, p. '75) has ysuggested visual examination vof grain by X-rays, and-Potter, G.;C. (Cereal Chem., 29, 223-1952) has described a spectro-photometrical method. Other workers'have kfound that some of these cereal pests carry volatile secretions which belong to a certain class of quinones. See Alexander, P. and Barton, YD.H.:'R., Biochem. 1 37, 463 (1943); Hackman, RH. et alibi'd. 43, .4.74 (1948,);fLacontLJfD. and Roth, L. M., Ann. Ent. Soc. Am., 46, 281 (719,53).

I have discovered that these quinones enter into chemical reactions .withlour proteins r,andthlat some of the quinonoid conjugates thus formed are fluorescent in ultravioletlightat veryllow concentrations. A method of detecting insect infestation by uorescence, in accordance with my invention, seems to be exceptionally well suited for the analysis of foodstus, since it is sensitive enough to cover the relatively small amounts of contamination generally involved and besides is inexpensive and may be quickly made by laboratory technicians of little experience. These are among the advantages of the invention.

In the accompanying drawings, Figs. 1 and 2 are graphs showing iluorescence intensities for extracts from samples of insect-contaminated wheat our.

The invention is best explained in connection with a description of actual procedures at the Quartermaster Pioneering Research Laboratories, Philadelphia Quartermaster Depot, U. S. Army. v

Insect-free, unbleached, hard, red, spring wheat our, specially prepared by a well-known mill in Minneapolis, Minn., was subjected to controlled contamination by flour beetles Tribolium confusum Duv. Two methods were employed. In method A, 5,000, 500, 50, 5 and 0 insects, respectively, were cultured by the method described by Ladisch, R. K. and McQue, B. in Science,

"ice

118, 324 (-1953), in one pound of the liour in each case, at 32 C. and 7'5 percent R. H. ,Duplicate cultures were maintained in this manner for two weeks. One set of the samples ('5) `,were then passed through a sieve line Venough to retain the larvae and beetles. The other set of samples, still containing the insects, were ground separately through a hammer mill, powdered Dry'lce being added during this operation to minimize volatilization ofLthe'insect quinones. VAfter the carbon dioxide had evaporated, Ajars containing the separate vsamples were sealed and vkeptin a compartment at 32 Cl for anotherweek to insure completion of the reaction between the 4llour and the insect quinones. All the jars were then placed in Yaffreezing compartment at 10 C. for three days to devitalize any eggs or larvae that may have survived. Thereafter, all :jars were kept tightly sealed at room temperature until used. i

Method B wasmuch the same except that 10 onepound oursamples were-treated with 500, 400, 300, 200, 100, 80, 50, 30, 10 and 0 beetles, respectively, prior to sieving Vor grinding. No Dry/Ice was used in the grinding operation. All 'ten sarnplesof method B were kept in tightly sealed jars at room temperature until used some weeks later.

YFor the iluorometric study, 4,grn. ysamples Vwere taken from each jar,.weighed accurately to 1:5 mg. Eachsample was extracted with 25.0 rnl. of a solvent consisting of 9 partsby volume of absolute Vencohol and 1 part of 15 N ammonium'hydroxide. Thesemixtures `wereeach shaken for ve minutes and centrifuged at high speed in a water-cooled centrifuge. The supernatant clear liquid was used directly formeasuring the iluorescence in the samples of tlour having 0 to 500 insects per pound, but was furtherdiluted with 2.5 parts ci thesolvent when ^analyzing themore VYhighly contaminated -our containing 5000 insects per pound. All glass equipment was employed throughout these .operations to prevent contamination of the samples with lluorescing material, e. g., rubber. i

'Fluorescence spectra were obtained with an automatic recording spectrophotometer with a fluorescence attachment. Measurements of the intensity of fluorescence were also made with Aa welldinown colorimeter with fluorescence accessories, including a sensitive triplebeam galvanometer. With each of these instruments, filters were employed to 'isolate the excitation radiation of 365 mu. *Secondary-filters were used when necessaryto exclude scatteredultraviolet radiation from the photocells. The colorirneter was adjusted to read for the'extractrom the mosthighly contaminated'sample in any series of measurements, the intensity or" uorescence of subsequent samples being referred to this basis. The measurements were made about three minutes after introducing the sample holder to allow the photocell to come to equilibrium. With the spectrophotometer, glass stoppered sample holders were used. The most highly contaminated sample of any series in this case was set at a value of 50 on the transmission dial; the data were later calculated to a basis of 100. Solvent as used for the extraction was set at zero uorescence by means of the dark current control. These settings were frequently checked with fresh portions of solvent and standards as stated. All manipulations were carried out rapidly to minimize errors arising from evaporation of the solvent. The iluoresceuce was blue-green, the wave length of the emitted radiation being 455i5 millirnicrons.

Referring to Fig. 1, here are shown uorometric data for wheat our extracts prepared as described above from samples contaminated by flour beetles Trfbolz'um confusum Duv. As explained above, the test samples respectively contained varying quantities of insects (be- Vtween S and 5000 insects) ground into each pound of Hour. Because of this wide range of numerical values, the data were plotted for convenience in a log-log ccordinate system. It will be observed that not only is there a consistent relationship between degrees of contamination up to 5000 beetles per pound andV fluorescence intensity, Vbut the presence of even beetles ground into oneY pound of our is clearly discernible. Compare the Yreading for the insect-free control sample, shown by the dotted line.

Fig. 2 shows fluorescence intensities of extracts of contaminated wheat flour prepared as described Yin the foregoing, with to 500 beetles ground into eachpound of our. The small open circles show the readings using the colorimeter with uorescenceaccessories, while Ythe small closed circles record the readings when using the spectrophotometer with fluorescence accessory set. Theseedata Were quite reproducible. Y

A particularly interesting inherent characteristic of the present method is the fact that it reveals insect contamination of iiour after most of the physical evidence of suchinfestation V(; e., the beetles, larvae and large fragments) had been removed. The pertinent data of samples, contaminated as described in the range of 10-500 insects per pound of ourand then puried by sieving, are arranged in the table following.

Table Fluorescence intensities of ammoniacal ethanol extracts of our contaminated with insects Trbolz'um confusum Y Duv. Flour samples were freed of beetles, larvae, and

large fragments prior Vto analysis. Instruments used: (a) Colorimeter; (b) spectrophotometer. Standard setting at 100.0.V

No.0fbeetles perpound of Y non: 500 400 300 200 100 so 50 30Y 10 0 (a)V 100.0 98.0 93.1 saasae 70.0 65.1 00.8 03.2 57.0 (b) 100.0 91.0 81.0 68.4 eso 05.8 75.4 52.2

as the number of insects decreases. The degree of dilution of the test samples is another important factor. It was noticed thatV undiluted our samples'showed a greater iluorescence intensity with 500 beetles than'with 5000 beetles, which may be due to a self-quenching effect, as'is Yknown to occur'with other uorescing substances at high concentrations. i i

Recently, I have found that a cysteine-insect quinon conjugate in slightly` ammoniacal r'water can be determined with a concentration of the substance as 10W asV V0.1 microgram/ml. ofV the substance. i This corresponds to approximately 0.05 Vmicrogram ofv quinone (5/100 of 1 millionth gram). The pertinent curve Was obtained with .a' Carey'rModel X1. automatic spectrophotometer. Conjugates of the insect quinone with amino acids, such as cysteine, are undoubtedly formed in the interaction Vbetween the flour and the beetle secretion.

and like protein-containing foodstuffs byV insects of the type that discharge volatilersecretions which belong to the class of quinones, which'con'sists in passing a sample of thecontaminated foodstui through a sieve tine enough to retain insects and larvae contaminatingrthe sample, extracting at least part of the sieved sample with a solvent consisting of nine parts by Volume of absolute alcohol and one partby'volume of 15 N ammonium hydroxide, shaking andthe centrifuging the mixture, thusY obtaining a clear liquid, Ymeasuring the fluorescence in Y' the clear liquid, and recording the value.

3. A process of detecting contamination of wheat our and like protein-containing foodstuffs byV insects of the typeV that discharge volatile secretions which belong to the class of quinones, which consists in grinding a sample of the contaminated foodstuff, extracting at least part of the ground sample with a ,solvent for fluorescent quinonoid materials in the sample,rshaking the mixture,Y

then obtaining a supernatant Vclear liquid, measurrV ing the fluorescence of said clear liquid, and recording the value.

References Cited in the file ofY patent Alexander and Barton: Biochemical Jo. vol. 37 (1943). pages 463-465.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No;1 2,82%364 Rolf Karl Ladisch March 18, 1958 It is hereby certified that 'error 'appearsin the abovewnumbered patent requiring correction and that the said Letters Patent should read as corfrected below..

`In the grant, lines l, 2 and 3y for "Rolf Karl 4Ladisch, of Lansdowne,

Pennsylvania," read -m Rolf Karl Ladisch, 'of Lansdowne, Pennsylvania,

assignor toA the United States of America asrepresented by the Secretary of the' Army, v==; line l2; for "Rolf Karl Ladisch, his heirs or assignsn Vread United States of America as represented by the Secretary of the Ar'my n; line l5, Ybeginning'with *'Provided', however, that 'the said" strike `out all to 'and including"t'lfl'ereon.,n in line 18; vin the heading to the vprinted specification, Yline 45 for Rolf Karl Ladisch, Lansdowne, Pao" read Rolf Karl Ladisch, Lansdowney Pa.,, 'assigner to the United States of America as'represented 'by lthe Secretary vof 'the .Army u; column lf, line 3l, for

"Drum" read n Drug column .Pg line 37 "the", first occurrence, read Signed and sealed this 24th day of June 1958A,1

(SEAL) Attest:

KARL H., AXLINE ROBERT (La WATSON Attesting Officer Commissioner of Patents 

1. A PROCESS OF DEFECTING CONTAMINATION OF WHEAT FLOUR AND LIKE PROTEIN-CONTAINING FOODSTUFFS BY INSECTS OF THE TYPE THAT DISCHARGE COLATILE SECRETIONS WHICH BELONG TO THE CLASS OF QUINOMES, WHICH CONSIST OF EXTRACTING A SAMPLE OF THE COMTAMINED FOODSTUFF WITH A SOLVENT FOR FLUORESENT IN THE SUPERNATANT CLEAR LIQUID OBTAINED FROM SAID EXTRACTION AND RECORDING THE VALUE. 